1. Field
Example embodiments relate to an image sensor which may include a sensing transistor having two gates and a method of operating the same, and more particularly, to an image sensor which may include a sensing transistor having two gates, wherein the image sensor may measure light intensity incident to a pixel by turning on the sensing transistor by applying a voltage to an additional gate when the sensing transistor is not turned on due to the strong light incident to the pixel, and a method of operating the same.
2. Description of the Related Art
An image sensor may be a photoelectric conversion device that may transform detected light into electrical signals. A conventional image sensor may include a plurality of unit pixels arranged in an array on a semiconductor substrate. Each of the unit pixels may include a photodiode and a plurality of transistors. The photodiode may generate optical charges in response to detected external light, and the transistors may output electrical signals according to the amount of the produced optical charges.
A complimentary metal oxide semiconductor (CMOS) image sensor may include a control device that may control and process optical signals. The control device may be manufactured using a CMOS manufacturing technique. The CMOS image sensor may have a simple manufacturing process, and a signal process device may be manufactured in a single chip together with a photodiode.
Studies have been conducted to increase a dynamic range of a CMOS image sensor. In particular, in an image sensor, when a light is incident to the image sensor, a potential of a floating diffusion region connected to a gate of a sensing transistor may be reduced, and a gate voltage may be reduced lower than a threshold voltage, thus a sensing voltage may not be detected, and thus, an optical intensity may not be acquired. In order to measure an optical intensity of a sensing transistor with a gate voltage below a threshold voltage, a logarithmic circuit may be used. In this case, however, the number of transistors may be increased and the linearity of the logarithmic circuit may be low. Thus, it may be difficult to correctly measure the optical intensity of strong light.
Therefore, there may be a need to develop a CMOS image sensor having a wide dynamic range to measure the optical intensity of strong light.